Recent developments in flow cytometry hardware and dye chemistry has made it possible to simultaneously measure as many as ten or more fluorescences and scattered light parameters from cells, beads, molecules, etc. herein referred to as particles. They provide a large amount of novel information, which permits identification and characterization of cell subsets. However, such multicolor prior art systems are complex and expensive. They require multiple optical paths and detectors and complex control circuits. They are not suitable for portable use, point of care use or battlefield use.
Conventional flow cytometers require hydrodynamic sheath flow to align the particles in a single line in the laser probe volume. The hydrodynamic focusing accelerates the sample and particles and requires relatively large volumes of sample and sheath fluid to carry out an analysis. Typically for sample volume flow rates of 1 μL /s and exit velocities of 25-50 mm/s the particle velocities reach 10 m/s when they cross the probe volume. For a probe beam laser width of 20 microns, the particle time of flight through the probe volume is 2 microseconds. Since the particle is present in the probe volume for only a short time, a detection system of relatively large bandwidth is required for each color thus leading to complex, expensive and bulky systems.